Existing flow distribution networks rely on symmetry, large components and close tolerances to distribute flows evenly to the branches. While this may be adequate for liquids or high pressure gases, the velocities experienced by low pressure compressible fluids amplify minor variations in fluidic elements, unbalancing the flows. This problem is particularly severe with complex geometries such as those found in shutoff valves.
Process sequences that alter gas flows with the plasma on, such as the one described in U.S. patent application Ser. No. 12/970,846 filed on Dec. 16, 2010 (hereby incorporated by reference in its entirety), generally require valves to be located as close to the process stations (e.g., chambers) as possible. This, in turn, requires the shutoff valves to be placed in each branch of the network, which can create a flow imbalance. Other applications, particularly those applications involving simultaneous gas flow to multiple stations in a reactor or multiple reactors, can also suffer flow imbalances to the individual stations or reactors.
Balancing flow rates using conventional technology requires symmetry across the branches, which may not be possible or desirable in some applications. For example, symmetry may preclude the use of highly variable fluidic elements such as conventional shutoff valves. Fabricating these fluidic elements to very low tolerances to maintain symmetry across the branches may be prohibitively expensive. Alternatively, using large components to balance flow requires a significant pressure drop in the system, which can increase cost and limit the maximum flow.